The present invention is generically directed on reception xe2x80x9clobexe2x80x9d shaping of a converter arrangement, which converts an acoustical input signal into an electrical output signal. Such a reception xe2x80x9clobexe2x80x9d is in fact a spatial characteristic of signal amplification, which defines, for a specific reception arrangement considered, the amplification or gain between input signal and output signal in dependency of spatial direction with which the acoustical input signal impinges on the reception arrangement. We refer to such spatial reception characteristics throughout the present description by the expression xe2x80x9cspatial amplification characteristicxe2x80x9d.
Such spatial amplification characteristic may be characteristically different, depending on the technique used for its shaping, for instance dependent from the fact whether the reception arrangement considered is of first, second or higher order.
As is well known from transfer characteristic behaviour in general, a first order arrangement has a frequency versus amplitude characteristic characterised by 20 dB per frequency decade slopes. Accordingly, a second order reception arrangement has 40 dB amplitude slopes per frequency decade and higher order reception arrangements of the order n, 20 n dB amplitude per frequency decade slopes. We use this criterion for defining respective orders of acoustical/electrical transfer characteristics.
The order of a reception arrangement may also be recognised by the shape of its spatial amplification characteristic.
In FIG. 1, there are shown three spatial amplification characteristics in plane representation of a first-order acoustical/electrical converting arrangement. The spatial amplification characteristic (a) is said to be of xe2x80x9cbi-directionalxe2x80x9d-type. It has equal lobes in forwards and backwards direction with respective amplification maxima on one spatial axis, according to FIG. 1 the 0xc2x0/180xc2x0 axis and has amplification zeros on the second axis according to the +90/xe2x88x9290xc2x0 axis of FIG. 1.
The second characteristic according to (b) shows an increased lobe in one direction as in the 0xc2x0 direction according to FIG. 1, thereby a reduced lobe characteristic in the opposite direction according to 180xc2x0 of FIG. 1. This characteristic is of xe2x80x9chyper-cardoidxe2x80x9d-type. The lobe of the spatial amplification characteristic may further be increased in one direction as in the 0xc2x0 direction of FIG. 1, up to characteristic (c), where the lobe in the opposite direction, i.e. the 180xc2x0 direction of FIG. 1 disappears. The characteristic according to (c) is named xe2x80x9ccardoidxe2x80x9d-type characteristic. Thus, xe2x80x9cbi-directionalxe2x80x9d and xe2x80x9ccardoidxe2x80x9d-types are extreme types, the xe2x80x9chyper-cardoidxe2x80x9d-type is in between the extremes.
At second and higher order reception arrangements the spatial amplification characteristics become more complicated having an increasing number of side-lobes. FIG. 2 shows one example of a second order amplification characteristic of cardoid-type.
In the EP 0 802 699 of the same applicant as the present application and which accords to the U.S. application Ser. No. 09/146 784 and to the PCT/IB98/01069, it is described in detail how a reception arrangement for acoustical/electrical signal conversion may be realised, with a desired spatial amplification characteristic. Thereby, two spaced apart acoustical/electrical converters, microphones, are of multi- or omni-directional spatial amplification characteristic. They both convert acoustical signals irrespective of their impinging direction and thus substantially unweighted with respect to impinging direction into their respective electrical output signals. To realise from such two-microphone arrangement a desired spatial amplification characteristic the output signal of one of the two microphones is time-delayed xe2x80x94xcfx84xe2x80x94, the time-delayed output signal is superimposed with the undelayed output signal of the second microphone.
It is further described, with an eye on FIG. 1 of the present application, how the time-delay xcfx84 is to be selected for realising bi-directional, hyper-cardoid or cardoid-type spatial amplification characteristics: For the time-delay xcfx84=0 the characteristic becomes bi-directional (a), by increasing xcfx84 the characteristic becomes hyper-cardoid, and finally becomes cardoid (c) if xcfx84 is selected as the quotient of microphone spacing xe2x80x94pxe2x80x94 to speed of sound, c. This technique, which has been known for long is referred to as xe2x80x9cdelay and superimposexe2x80x9d technique.
In this literature, which is to be considered as an integral part of the present invention by reference, it is further described how spatial amplification characteristic shaping may be improved, following the concept of electronically i.e. xe2x80x9cvirtuallyxe2x80x9d controlling the effective spacing of the converters without influencing their physical xe2x80x9crealxe2x80x9d spacing.
First-order reception arrangements for acoustical input signals and especially when realised with a pair of omni-directional converters, as of microphones and as described in detail in the above mentioned literature, have several advantages over higher order reception arrangements. These advantages are especially:
simple electronic structure and small constructional volume, which is especially important for miniaturised applications as e.g. for hearing aid applications,
low cost,
low sensitivity to mutual matching of the converters used, as of the microphones,
small roll-off, namely of 20 dB per frequency decade.
Nevertheless, such a reception arrangement, as mentioned construed of two multi- or omni-directional converters has disadvantages, namely:
The maximum theoretical directivity index DI is limited to 6 dB, in practise one achieves only 4 dB to 5 dB. With respect to the definition of the directivity index DI please refer to speech communication 20 (1996), 229-240, xe2x80x9cMicrophone array systems for hand-free telecommunicationsxe2x80x9d, Garry W. Elko.
It is an object of the present invention to quit with the disadvantages mentioned above, thereby keeping the advantages. Although the present invention departs from advantages and disadvantages of first order reception arrangements directed on acoustical signal treatment, it must be emphasised that once the inventive concept has been recognised, principally it may be applied to other types of reception arrangements, as to higher order reception arrangements.
To resolve the above mentioned object the present invention proposes a method for shaping the spatial amplification characteristic of an arrangement which converts an acoustical input signal to an electrical output signal and wherein, as was mentioned above, the spatial amplification characteristic defines for the amplification with which the input signal impinging on the arrangement is amplified, as a function of its spatial impinging angle, to result in the electrical output signal.
The inventive method thereby further comprises the following steps:
There are provided at least two sub-arrangements with at least one converter which sub-arrangements each convert an acoustical input signal to an electrical output signal, but which sub-arrangements have different spatial amplification characteristics.
There are generated at least two first signals which are proportional to the output signals of the sub-arrangements, in frequency domain and with a number of spectral frequencies.
There are further generated at least two second signals which are proportional to the output signals of the sub-arrangements, in frequency domain, and with said number of said spectral frequencies. Thus, the first and second signals may, but need not be equal.
The magnitudes of spectral amplitudes of the at least two first signals at equals of said spectral frequencies are compared, there results for each spectral frequency mentioned one comparison result. By these xe2x80x9cspectralxe2x80x9d comparison results one controls, which of the spectral amplitudes of the second signals at respective ones of the spectral frequencies mentioned is passed to the output of the arrangement.
Thereby, it principally becomes possible to combine the advantages of either of the at least two specific spatial amplification characteristic of the sub-arrangements so that the combination exploits that spatial amplification characteristic which is more advantageous in a predetermined spectral angular range, thereby quitting its disadvantages by selecting the second amplification characteristic to be active in a further spectral angular range, there exploiting the advantages of the second characteristic.
In a most preferred mode comparison is performed to indicate as a result, which of the spectral magnitudes at a respective frequency is smaller than the other. Thereby and in a further preferred mode, the second signal spectral amplitude is passed which accords with the smaller magnitude of the magnitudes being compared.
In a further most preferred mode of realisation the at least two sub-arrangements of converters are realised with one common set of converters and the different amplification characteristics requested are realised by different electric treatments of the output signals of the converters. As in a most preferred form of realisation, the above mentioned xe2x80x9cdelay and superimposexe2x80x9d-technique is used, e.g. from two specific converters and with implying in parallel two or more than two different time delaysxe2x80x94xcfx84xe2x80x94, two or more different amplification characteristics may be realised e.g. just with one pair of converters.
Further preferred modes of operation of the inventive method will become apparent from the following detailed description of examples of the present invention and are specified in the dependent method claims.
So as to resolve the above mentioned object there is further proposed a reception arrangement which comprises at least two converter sub-arrangements, which each converts an acoustical input signal to an electric output signal at the outputs of the sub-arrangements respectively.
There is further provided a comparing unit with at least two inputs and with an output. This comparing unit compares magnitudes of spectral amplitudes at spectral frequencies of a signal applied to one of its inputs with magnitudes of spectral complitudes at respective equal frequencies of a signal applied to the other of its inputs. Thereby the comparing unit generates a spectral comparison result signal at its output. The outputs of the at least two sub-arrangements are operationally connected to the at least two inputs of the comparing unit.
There is further provided a switching unit with at least two inputs, a control input and an output. The switching unit switches spectral amplitudes of a signal applied at one of its inputs to its output, controlled by a spectralxe2x80x94binaryxe2x80x94signal at its control input. The signal at the control input frequency-specifically controls which one of the at least two inputs of the switching unit is the said one input to be passed. The output of the comparing unit is thereby operationally connected to the control input of the switching unit, the at least two inputs of the switching unit are operationally connected to the outputs of the at least two sub-arrangements.
Preferred embodiments of such inventive converter arrangement will become apparent to the skilled artisan when reading the following detailed description and are further defined in the dependent apparatus claims.
Thereby, the inventive apparatus and method are both most suited to be realised as shaping method implied in a hearing aid apparatus and as a hearing aid apparatus respectively.